1. ME 475/675 Introduction to Combustion
Lecture 10
Next year give next lecture here and this lecturer next time. Ask students to attempt HW before coming to this lecture
Examples using Computer Programs and Constant Specific Heats

2. Announcements FALL 2017 CAREER FAIR Midterm 1 HW 4
Thursday, September 28
Learn more about career services
Midterm 1
October 2, 2017
HW 4
Due Friday (I’ll accept it Monday)
Ch 2 (33, 47, 57, 50, 54, 63)

3. Problem 2.47 (homework)
Calculate the equilibrium composition for the reaction 𝐻 𝑂 2 ↔ 𝐻 2 𝑂 when the ratio of the number of moles of elemental hydrogen to elemental oxygen is unity. The temperature is 2000 K, and the pressure is 1 atm.
Extra:
What will happen to the amount of 𝐻 2 if the pressure is decreased?
At what pressure will 𝜒 𝐻 2 =0.01?

4. Problem 2.50 (homework)
Reformulate problem 2.47 to include the species OH, O, and H. Identify the number of equations and the number of unknowns. They should of course be equal. (Write a system of equations that can be used to solve for the unknowns). Do not solve your system.

5. Problem 2.54 (Homework)
Consider the combustion of decane (C10H22) with air at an equivalence ratio of 1.25, pressure of 1 atm, and temperature of K. Estimate the mixture composition assuming no dissociation except for the water-gas shift equilibrium. Compare with results of TPEQUIL.
Hint: Hydrocarbon Combustion with Shift Reaction Equilibrium MathCAD Solution

6. Problem 2.63 (Homework)
A furnace uses preheated air to improve its fuel efficiency. Determine the adiabatic flame temperature when the furnace is operating at a mass air-fuel ratio of 16 for air preheated to 600 K. The fuel enters at 200 K.
Assume the following simplified thermodynamic properties: Tref = 300 K, MWfuel = MWair = MWprod = 29 kg/kmol; cp,air = cp,prod = cp,fuel = 1200 J/kg-K; ℎ 𝑓,𝑎𝑖𝑟 𝑜 = ℎ 𝑓,𝑝𝑟𝑜𝑑 𝑜 =0; ℎ 𝑓,𝑓𝑢𝑒𝑙 𝑜 =4∗ 10 7 𝐽/𝑘𝑔

7. Problem 2.33 (Homework)
Once more, repeat problem 2.30, but eliminate the unrealistic assumptions, i.e. allow for dissociation of the products and variable specific heats. Use HPFLAME (Appendix F), or other appropriate software. Compare and contrast the results of problems 2.30 to Explain why they differ.
2.30 Determine the adiabatic flame temperature for constant- pressure combustion of a stoichiometric propane-air mixture assuming reactant at 298K, no dissociation of the products, and constant specific heats evaluated at 298K.

9. Problem 2.35 (homework)
Repeat problem 2.30, but for constant-volume combustion. Also, determine the final pressures.
Add, compare results with UVFLAME

10. Computer Programs Provided by Book Publisher
Described in Appendix F
For “complex” reactions (11 product species)
Fuel: CNHMOLNK
Oxidizer: Air
Download from web:
student edition
Computer codes
Access to TPEquil, HFFlame, UVFlame
Extract All
TPEQUIL (TP Equilibrium)
Use to find
Equilibrium composition and mixture properties
Required input
Fuel CNHMOLNK
Temperature
Pressure
Equivalence ratio (with air)
to determine initial number of moles of each atom

11. HPFLAME (HP Flame) Use to find Required Input
Adiabatic flame temperature for constant pressure
Required Input
Fuel, equivalence ratio, enthalpy of reactants HR, pressure
For constant pressure: HP = HR
Find TAd
In our examples we assume ideal combustion so we knew the product composition
But this program calculates the more realistic equilibrium composition of the products from a (complex) equilibrium calculation (multiple equilibrium reactions)
But this requires TProd = TAd, which we are trying to find!
Requires program (not humans) to iterate